Generally, a typical scanning apparatus has a single sensing element and a single lens for capturing an image of a document. The conditions of the sensing element and the single lens contained in the scanning apparatus are preset to achieve a suitable resolution. That is, the scanning performance is optimized when the document is scanned under the designed resolution. For scanning the document under a different resolution, another scanning apparatus having a desired resolution is necessary. That is, the conditions of the sensing element and the lens of a specified scanning apparatus which are suitable for scanning A4-sized documents are usually improper to scan A3-sized documents. Under this circumstance, another scanning apparatus with a different set of sensing element and lens and having a desired resolution for the A3-sized documents should be offered. For example, although the scanning apparatus which is suitable for scanning A3-sized documents can scan A4-sized documents, the scanned images are usually blurred and unacceptable because the resolution is insufficient. On the other hand, the scanning apparatus which is suitable for scanning A4-sized documents fails to be used for scanning A3-sized documents because the size of the A3-sized document is greater than the glass platform of the scanning apparatus. In addition, since the width of the A3-sized document is very large (e.g. 297 mm), the optical path length is increased and thus the resolution of the scanned images is reduced. Under this circumstance, the scanned images are also blurred. For solving the above problems, some commercial scanning apparatuses with different resolutions have been proposed.
For example, a scanning apparatus with diverse resolution is described in Taiwanese Patent No. 00488143. Referring to FIG. 1, a schematic partial view of such a scanning apparatus is illustrated. The scanning apparatus of FIG. 1 principally includes a first rotational disk 1, a second rotational disk 2, a spindle 3, a transmission shaft 4 and a motor 5. The first rotational disk 1 has a plurality of lenses 11a, 11b, 11c and 11d, which are located in the first rotational disk 1 and arranged in an annular manner. Please refer to FIG. 2 and FIG. 3. The second rotational disk 2 has a plurality of charge-coupled devices (CCDs) 21a, 21b, 21c and 21d, which are located in the second rotational disk 2 and arranged in an annular manner. These charge-coupled devices have different resolutions.
Please refer to FIG. 1 again. The spindle 3 penetrates through centers of the first rotational disk 1 and the second rotational disk 2 and is rotatable. The transmission shaft 4 penetrates through a first one-way shaft bearing 41a and a second one-way shaft bearing 41b such that the first one-way shaft bearing 41a and the second one-way shaft bearing 41b are rotatable. In addition, the first one-way shaft bearing 41a and the second one-way shaft bearing 41b are respectively engaged with the outer rims of the first gear teeth 12 of the first rotational disk 1 and the second gear teeth 22 of the second rotational disk 2. The transmission shaft 4 has one end attached to a shaft gear 42, which is engaged with a transmission gear 51 of a motor 5. By means of the above linking mechanism, the first rotational disk 1 and the second rotational disk 2 are rotated once the motor 5 is activated. The first rotational disk 1 and the second rotational disk 2 are rotated in opposite directions because the first one-way shaft bearing 41a and the second one-way shaft bearing 41b have opposite rotation directions. In other words, the transmission shaft 4 is rotated in only one direction, but the first one-way shaft bearing 41a and the second one-way shaft bearing 41b on the transmission shaft 4 in opposite directions.
FIG. 4 schematically shows the structure of the one-way shaft bearing of the conventional scanning apparatus. As shown in FIG. 4, the one-way shaft bearing includes an outer tube 81, a plurality of gear teeth 811, a plurality of rollers 82 and an inner tube 83. The rollers 82 are located between the outer tube 81 and the inner tube 83. A plurality of taper wedge members 812 are attached on the inner surface of the outer tube 81. Each roller 82 is located between two adjacent wedge members 812. When the gear teeth 811 on the outer peripheral of the outer tube 81 is driven to rotate in an anti-clockwise direction, the rollers 82 will roll along the surfaces of the wedge members 812 without hindrance an thus the inner tube 83 cannot be driven to rotate in an anti-clockwise direction. In other words, the anti-clockwise rotation of the outer tube 81 results in idle running of the inner tube 83. On the other hand, when the gear teeth 811 on the outer peripheral of the outer tube 81 is driven to rotate in a clockwise direction, the rollers 82 will be retained by the wider edges of the wedge members 812 an thus the inner tube 83 will be driven to rotate in a clockwise direction. In other words, the outer tube 81 and the inner tube 83 are simultaneously driven to rotate. As shown in FIG. 1, the one-way shaft bearing 41a and 41b mounted on the transmission shaft 4 have the same structures but are arranged in reverse directions. When the motor 5 rotates in a clockwise direction to drive rotation of the first rotational disk 1, the second rotational disk 2 will remain stationary. Likewise, when the motor 5 rotates in an anti-clockwise direction to drive rotation of the second rotational disk 2, the first rotational disk 1 will remain stationary. In other words, no matter what direction the motor 5 rotates, only one of the first rotational disk 1 and the second rotational disk 2 is driven to rotate.
Please refer to FIG. 1 again. By rotating the first rotational disk 1, one of the lenses 11a, 11b, 11c and 11d may be moved on the optical path of the scanning apparatus to pair with a selected CCD (such as 21a) for obtaining different combinations of resolution. Likewise, by rotating the second rotational disk 2, one of the CCDs 21a, 21b, 21c and 21d may be moved on the optical path of the scanning apparatus to pair with a selected lens (such as 11a) for obtaining different combinations of resolution. If necessary, the motor 5 is rotated in clockwise and anti-clockwise directions, one of the lenses 11a, 11b, 11c and 11d of the first rotational disk 1 is moved on the optical path of the scanning apparatus to pair with one of the CCDs 21a, 21b, 21c and 21d of the second rotational disk. Through this arrangement, a wide range of resolutions may be obtained.
Although the scanning apparatus with diverse resolution as described above may alleviate the drawback of using the single-resolution scanning apparatus, there are still some problems. For example, the rotational disks are engaged with the corresponding one-way shaft bearings through engagement of corresponding gear teeth and the rotational disks are controlled to rotate through the gear teeth. Due to unmatched engagement of gear teeth, erroneous operation of the adjusting the resolution readily occurs. Moreover, during the scanning operation, the selected lens and the selected CCD should be precisely aligned with each other by rotating the rotational disks. As known, it is time-consuming to precisely align the selected lens with the selected CCD. As the scanning apparatus has been used for a long term, the accuracy of precise alignment will be impaired because the gear teeth are readily abraded. Under this circumstance, it is difficult to align the selected lens with the selected CCD and move the selected lens with the selected CCD on the optical path.
Therefore, there is a need of providing an improved scanning apparatus with different resolutions.